The present invention relates to a color sensor including a photoelectric semiconductor device and, more particularly, to a wavelength detection system responding to output signals derived from a dual junction photoelectric semiconductor device including at least two PN junctions formed at different depth from the surface of the semiconductor device.
It is well known in the art that the photoelectric conversion phenomenon is observed when a light beam impinges on a semiconductor device including a PN junction. This photoelectric conversion phenomenon is utilized in various semiconductor devices such as photodiodes, phototransistors and solar batteries.
The light absorption factor is greatly influenced by the material of the semiconductor substrate and the wavelength of the light beam impinging thereon. A light beam of a shorter wavelength is absorbed near the surface of the semiconductor substrate, whereas a light beam of a longer wavelength reaches a deeper section of the substrate.
Therefore, when a photoelectric semiconductor device including at least two PN junctions formed at different depth from the surface of the semiconductor substrate is constructed, an output signal derived from a PN junction formed at a shallower section may represent the shorter wavelength component of the impinging light beam, and an output signal derived from a PN junction formed at a deeper section may represent the longer wavelength component of the impinging light beam.
Accordingly, an object of the present invention is to provide a wavelength detection system implemented with a photoelectric semiconductor device.
Another object of the present invention is to provide a solid state color sensor including a dual junction photoelectric semiconductor device having at least two PN junctions formed at different depths from the surface of the semiconductor substrate.
Still another object of the present invention is to provide a color difference measuring instrument responsive to output signals derived from a solid state wavelength detection system.
Yet another object of the present invention is to provide a light source output level control system including a solid state wavelength detection system.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a photoelectric semiconductor device is constructed to have at least two PN junctions formed at different depths from the surface of the semiconductor substrate. A first output signal derived from a deeper PN junction mainly represents the longer wavelength component of the light impinging on the photoelectric semiconductor device. A second output signal derived from a shallower PN junction mainly represents the shorter wavelength component of the impinging light.
In a preferred form, a first output signal is applied to a first logarithmic compression circuit, and a second output signal is applied to a second logarithmic compression circuit, respectively. Output signals of the first and second logarithmic compression circuits are applied to an operation amplifier to compare or substract the two output signals derived from the logarithmic compression circuits with each other. That is, the wavelength of the impinging light is detected by comparing the levels of the two output signals derived from the deeper PN junction and the shallower PN junction.